1. Field of the Invention
The present invention relates to a fuel cell system, which recycles water from an exhausted liquid of a fuel cell stack thereof.
2. Description of the Related Art
A direct methanol fuel cell (DMFC) is one of various types of fuel cells and capable of directly utilizing methanol as a fuel without reforming. The direct methanol fuel cell is ordinarily provided with a fuel cell stack, which includes one or more fuel cells. Each of the fuel cells is provided with a membrane electrode assembly (MEA), which is composed of a cathode catalyst layer, a cathode gas diffusion layer, an anode catalyst layer, an anode gas diffusion layer and an electrolyte membrane put between a cathode catalyst layer and an anode catalyst layer. A mixture of the methanol and water is supplied to the anode and air is supplied to the cathode. As a result of reaction in the fuel cell, water is generated and exhausted from the cathode.
The water is necessary for generating the reaction in the DMFC and for this purpose the water generated in the reaction is sometimes recycled. Japanese Patent Application Laid-open No. 2002-110199 discloses a related art, in which the water exhausted from the cathode is recycled. According to this related art, the fuel cell system is provided with a mixing tank and the recycled water and fuel supplied from a fuel tank is mixed to form a mixture therein. The recycled water contained in the mixture is supplied to the anode of the DMFC. However, the recycled water has relatively high temperature and causes an increase in temperature of the mixture in the mixing tank. The increase in temperature leads to an increase in loss of methanol since vapor pressure thereof increases and the vaporized methanol is lost in an exhaust from the mixing tank.